Keep in mind that the Felines dont have too many upgrade paths, so you might get stuck if you want to build on them
Mishras Burnished Banner has some interesting and powerful cards that could find their place in a competitive environment, but youd have to build a completely new deck around them rather than simply upgrading the precon
Then each creature that isn't an Insect, Rat, Spider, or Squirrel gets -1/-1 until end of turn for each creature you control that's an Insect, Rat, Spider, or Squirrel
Sure it gets exiled after, but free is a deep discount and four mana for a large spell isnt anything to sneeze at either
Summary In summary, the process of making custom Magic: The Gathering cards is truly enchanting